1. Field of the Invention
This invention relates to a power supply unit and an electric vehicle incorporating the same.
2. Prior Art
Conventionally, as a power supply unit of this kind, a power supply circuit for an automotive vehicle has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 51-7451, which changes over the manner of connection of a plurality of batteries to supply electric power demanded by a starter of an internal combustion engine installed on an automotive vehicle. This power supply unit circuit includes two batteries each having an output voltage of 12 volts. The batteries are connected in series at the start of the engine to apply a voltage of 24 volts to the starter, whereas after the start of the engine, the batteries are connected in parallel to apply a voltage of 12 volts to other electric devices of the engine.
Further, a power supply unit has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 7-87687, which uses electric double-layer capacitors as a power source and supply power derived therefrom to an electrical appliance, such as a table lamp and a word processor, via a switching regulator.
However, the former employs two batteries, but does not employ a plurality of low-capacity electric double-layer capacitors connected in series. Therefore, the proposed electric circuit is not adapted to change the manner of connection of low-capacity capacitors to take out a necessary amount of power therefrom.
On the other hand, the latter is directed to a power supply unit for supplying electric power to an electrical appliance which consumes an almost constant amount of power, but not to one for an electric vehicle or the like of which the electric power consumption sharply fluctuates.
Further, if electric double-layer capacitors which are generally large in internal resistance are used in a power supply unit of an electric vehicle which consumes a large amount of electric power, there would arise a problem that an amount of heat generated within the capacitors is too large for the power supply unit to generate a sufficient output.